Objectives: The broad objectives of this proposal are concerned with Occupational Health. They are: a) to formulate patterns of intermittent work and heat exposures on the basis of the physilogic mechanisms that underlie the adjustments of men to work in the heat; b) to psychrometrically define the safe limit of heat exposure by assessing the physiologic strain in men exposed to various levels of heat stress; c) to find a brief simple, heat tolerance test; and d) to establish an efficient method for heat acclimation. The specific aims are to expose working men and women to high air temperatures and radiant heat with increase in vapor pressure, to schedule intermittent exposures to heat with different combinations of work loads and rest periods and to reduce the heat exposure in the acclimation procedure by increasing exercise in temperate environment. Controlled laboratory studies will simulate industrial jobs involving heat exposure. Body temperatures, heart rate, sweating and subjective evaluation of discomfort and fatigue will be determined. Our general approach involves testing tolerance and adjustment to heat, using the criteria of elevation of physiologic responses above that expected under the nonstressing conditions. By applying gradual changes in vapor pressure a safer approach than the conventional, acute stress testing could be used to find the llmit of tolerance. Our informatioj on the adjustments to heat, the duration of exposure and recovery and improved acclimation methods coul be applied to controlling exposure for safety and well-being of workers.